1. Field of the Invention
The present invention relates to an exposure method and an exposure apparatus which are suitable for use in the production of semiconductor devices. More particularly, the present invention is concerned with an exposure method and an exposure apparatus which enable precise and rapid projection of delicate circuit patterns for, for example, an integrated circuit (IC) or a large-scale integrated circuit (LSI) carried by a reticle onto a semiconductor wafer through a projecting optical system, thereby exposing the wafer to the image of the circuit pattern.
2. Description of the Prior Art
The current semiconductor production technology is experiencing a trend toward a higher degree of integration and fineness of the circuit pattern. Optical exposure techniques for achieving such a high degree of integration and fineness of the circuit pattern have made remarkable progress by virtue of, for example, development of projecting optical systems having high resolution.
Production of semiconductor devices through optical exposure requires that a circuit pattern on the surface of a reticle be transferred to and printed on the surface of a wafer, which essentially requires projection of the circuit pattern image on the wafer surface with high precision, i.e., by focusing the image on the wafer with high precision.
However, in the conventional exposure method, one of a reticle and a wafer is moved relatively to the other while the condition of focus of the circuit pattern image on the wafer is observed through an observation system. The movement is stopped when the circuit pattern image is focused. After that, the wafer surface is exposed to print the circuit pattern thereon. This conventional method, therefore, suffers from an impractically low throughput.
In addition, printing of a multiplicity of circuit patterns on a wafer requires repetition of the precise focusing operation several times, and thereby requires much labor and time.